Generally, in nuclear power generation, thermal energy is generated by the chain fission of a fissionable material (e.g., thorium, uranium, and plutonium), and power necessary for electric power generation is derived from the thermal energy. The fissionable material is typically prepared in the form of a sintered body and contained in a nuclear fuel rod. Nuclear fuel rods are arranged in a bundle to form a nuclear fuel assembly. In a nuclear reactor, a control rod and a moderator are generally used to control the number and speed of extra neutrons and prevent a chain reaction (reactivity:>1) of fissionable materials. The moderator can include heavy water (D2O), light water (H2O), graphite, and beryllium, for example. Nuclear reactors may be classified into types depending on the nature of the moderator. For example, light-water nuclear reactors (LWR) include pressurized water reactors (PWR) and boiling water reactors (BWR). Other types of nuclear reactors include heavy-water nuclear reactor (HWR), which include a heavy water moderator, and high-temperature gas-cooled reactors (HTGR).
Emergency shutdown procedures are critical for safety in nuclear power plants. To stop a nuclear reactor, control rods formed of solid neutron poison materials (e.g., zirconium hydride) are generally inserted into a core. Emergency core cooling systems are also required for nuclear reactors. The emergency core cooling system functions to stop operations of the nuclear reactor and to prevent an increase in temperature of the nuclear reactor. An emergency core cooling system typically includes a supply of an aqueous solution including soluble boron. Typically, the emergency pool typically contains a boric acid solution or, in some cases, a sodium pentaborate solution that is pumped into the reactor to quench the fission reaction.